The present invention relates to a hydraulic damper arrangement with a hydraulic positive-displacement unit. More particularly, the present invention is directed to a hydraulic damper in the form of a piston/cylinder unit and insertable between an element to be damped in terms of its movement and a relatively stationary element. The arrangement has in its housing two chambers which are connected to one another via at least one channel with a throttle effect and between which hydraulic medium is exchanged via the channel during the shifting of the positive-displacement means.
A damper arrangement is shown, for example, in German Patent Specification 939,657. Here, a positive-displacement means is formed by a piston which, within the cylinder, separates two chambers connected to one another via channels passing through the piston. At the same time, one group of channels interacts with plate valves arranged on the piston top side and another group of channels interacts with the plate valves arranged on the piston underside. The valve plates on the piston top side are assigned a first helical spring which is arranged between the piston top side and the upper portion of the cylinder. The valve plates on the underside are assigned a further helical spring which is inserted between the piston underside and the lower portion of the cylinder. Furthermore, the chamber arranged between the upper portion of the cylinder and the piston topside is also connected to a compensating chamber. At the same time, a flow from the one chamber into the compensating chamber has to overcome the closing pressure of a non-return valve opening in this direction, and a flow in the opposite direction from the compensating chamber into the one chamber goes via a plate valve opening in this flow direction.
The above-described arrangement of the plate valves located on the piston ensures that only a relatively low or vanishing damping resistance has to be overcome when the piston leaves the middle position in relation to the cylinder; in contrast, during the return of the piston to its middle position, a markedly increased damping resistance has to be overcome. Furthermore, the springs loading the plate valves located on the piston also exert some adjusting force which seeks to urge the piston into it middle position.
German Offenlegungsschrift 3,808,996 shows a hydraulically damping two-chamber engine bearing which is designed in the manner of a positive-displacement unit. In this, the housing possesses two chambers communicating with one another via a channel and a positive-displacement device which is arranged movably within the one chamber and which is connected elastically to the positive-displacement housing via a suspension spring. On the positive-displacement device, a canceling mass is arranged vibrationally within one chamber. Furthermore, an elastic diaphragm is arranged as a partition between the two chambers. The canceling mass reduces the dynamic rigidity of the engine bearing within a limited frequency range. An uncoupling during high-frequency vibrations can be obtained by the diaphragm between the two chambers.
In practice, there is often a need for damper arrangements having a behavior with a pronounced frequency selectivity. For example, in a steering damper, it is desirable that the damper should oppose only a slight resistance to the normal steering movements, but undesirable vibrations will be damped sharply. While steering movements take place at relatively moderate speed, the undesirable vibrations in the steering system of the vehicle are usually around approximately 10 Hz to 25 Hz. Moreover, in a steering damper, it is also desirable that high-frequency vibrations should, if possible, not be transmittable.
An object of the present invention is, therefore, to provide a hydraulic damper arrangement having a behavior with a pronounced frequency selectivity, while at the same time a good uncoupling between the inlet and outlet of the damper arrangement will be guaranteed during high-frequency vibrations.
According to the present invention, this object is achieved in that the positive-displacement device or the housing is vibrationally connected, via an elastic spring mounting arranged in series therewith, to the element to be damped. The spring constant of the spring mounting, the mass of that part (positive-displacement device or housing) of the damper arrangement connected to the spring mounting, the mass of the hydraulic medium moved during relative movements between the positive-displacement device and the housing, and the ratio between the cross-section of the positive-displacement device are calculated in such a way that the resonant frequency of vibrations of these masses in relation to the stationary part of the damper arrangement is near the frequency range of undesirable vibrations of the element to be damped. The channel or channels have a throttle resistance increasing sharply, i.e., super proportionally, with the flow velocity.
In the damper arrangement according to the present invention, therefore, movable masses are vibrationally coupled via the spring mounting t the part to be damped in terms of its movement, in such a way that the vibrational masses can be excited by the element to be damped in terms of it movement with the flow of velocity into resonant vibrations which, due to their high speed of movement, lead to high flow velocities of the hydraulic medium in the channel or channels, so that their throttle effect gives rise to a high dissipation of energy, that is to say a large amount of kinetic energy is extracted from the element to be damped in terms of its movement.
When the relative movements between the positive-displacement device and the housing are very slow, the elasticity of the spring mounting and the throttle resistance of the channel or channels can be largely ignored. In other words, the element to be damped in terms of its movement and the relatively stationary element can be moved in relation to one another virtually without any resistance.
When vibrations of very high frequency, that is to say of a frequency well above the resonant frequency, act on the damper arrangement, the stationary part of the damper arrangement, on the one hand, and the masses vibratable relative to this, on the other hand, are substantially uncoupled vibrationally from one another by means of the spring mounting, with the result that the volumetric flow of hydraulic medium passing through the channel or channels decreases sharply, the amount of energy dissipation becoming correspondingly small or approach zero. The spring mounting thus prevents high-frequency vibrations from being transmitted between the element to be damped in terms of its movement and the stationary element. The acoustic transmission of noises between the element to be damped in terms of its movement and the stationary element can as far as possible be prevented in this way. The channel or channels from a throttle arrangement which can be located, for example, in the positive-displacement means or piston.